Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session Q15: TeV Gamma RaysRecordings Available
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Sponsoring Units: DAP Room: Marquis C |
Monday, April 11, 2022 10:45AM - 10:57AM |
Q15.00001: Improving the Search for Primordial Black Holes with HAWC Kristi L Engel Primordial Black Holes (PBHs) are black holes that may have been created by density fluctuations in the early Universe and could be as massive as supermassive black holes or as small as the Planck scale. It is believed that a black hole has a temperature inversely proportional to its mass and will thermally emit all species of fundamental particles via Hawking Radiation. PBHs with initial masses of ~5e14 g should be expiring today, producing bursts of high-energy gamma radiation in the GeV--TeV energy range. The High-Altitude Water Cherenkov (HAWC) Observatory is sensitive to particles with energies of ~300 GeV to above 100 TeV, which corresponds to the high end of the PBH burst spectrum. With its large instantaneous field of view of ~2 sr and a duty cycle above 95%, the HAWC Observatory is ideally suited to perform searches for PBH bursts. We advanced HAWC's already world-leading data-driven limit on the burst rate density of PBHs to incorporate extended durations to search and combined limits, as well as to take advantage of recent structural and algorithmic upgrades to the Observatory. |
Monday, April 11, 2022 10:57AM - 11:09AM |
Q15.00002: Limits on the Diffuse Gamma-Ray Background with HAWC Mora Durocher The high-energy Diffuse Gamma-Ray Background (DGRB) is expected to be produced by unresolved extragalactic objects and potentially dark matter annihilation or decay emissions in galactic or extragalactic structures. The DGRB has only been observed below 1 TeV and above this energy, upper limits have been reported. Observations or stringent limits on the DGRB above this energy could have significant multi-messenger implications, such as constraining the origin of TeV-PeV astrophysical neutrinos detected by IceCube. The High Altitude Water Cherenkov (HAWC) Observatory, located in central Mexico at 4100 m above sea level, is sensitive to gamma rays from a few hundred GeV to several hundred TeV and continuously observes a wide field-of-view of 2 sr. With its high-energy reach and large area coverage, HAWC is well-suited to notably improve searches for the DGRB at TeV energies. In this work, strict cuts have been applied to the HAWC dataset to better isolate gamma-ray air showers from background hadronic showers. The sensitivity to the DGRB was then verified using 535 days of Crab data and Monte Carlo simulations, leading to new limits above 10 TeV on the DGRB with HAWC as well as prospective implications for multi-messenger and dark matter studies. |
Monday, April 11, 2022 11:09AM - 11:21AM |
Q15.00003: Searching for Extragalactic TeV Sources Kara Whitaker, Miguel A Mostafa, Hugo Ayala We search for very-high-energy emission from extragalactic sources using six years of data from the High Altitude Water Cherenkov (HAWC) observatory. We use a published prescription to define a list of candidates from relatively nearby extragalactic radio-emitting X-ray sources. If no significant excess is found in the HAWC data, we determine flux upper limits at TeV energies using different empirical functions to extrapolate the spectra. We also use our analysis to constrain the physical parameters of the sources (e.g., energy cutoff, spectral index, etc.). We identify and present possible interesting candidates for further studies. |
Monday, April 11, 2022 11:21AM - 11:33AM |
Q15.00004: Studies of Galactic Cosmic-Ray Accelerators with VERITAS Brian Humensky Supernova remnants (SNRs) and pulsar wind nebulae (PWNe) are key classes of Galactic particle accelerators and are generally thought to be responsible for providing the bulk of cosmic rays in the Galaxy up to the knee. VERITAS observations of SNRs and PWNe in the very high energy (VHE; E > 100 GeV) range provide critical information to help us understand the nature of these accelerators, including the types of particles (leptons, hadrons, or a mix?) responsible for their VHE emission, as well as the maximum energies which they can reach. VERITAS, as an array of four imaging air Cherenkov telescopes, also provides sufficient angular resolution to correlate VHE emission with gamma-ray emission at higher (HAWC, LHAASO) and lower (Fermi-LAT) energies, as well as potential counterparts - whether compact objects, molecular clouds, or other structures - observed at other wavelengths. In this talk, we will summarize recent results from VERITAS, focusing on updated gamma-ray maps and spectra for IC 443, a resolved gamma-ray SNR interacting with molecular and atomic clouds in its vicinity. |
Monday, April 11, 2022 11:33AM - 11:45AM |
Q15.00005: Investigating the origins of TeV gamma-ray emission of MGRO J1908+06 with VERITAS Ruo Yu Shang MGRO J1908+06 is a bright TeV gamma-ray source. Since its discovery by the Milagro water Cherenkov telescope, it has been detected by H.E.S.S., VERITAS, ARGO-YBJ, HAWC, and Fermi-LAT. Despite the evident detections in the TeV regime, searches for a counterpart in the radio and X-ray domains have been unsuccessful, and the nature of the TeV gamma-ray production remains unknown. The accelerator candidates in the vicinity include PSR J1907+0602 (leptonic contributor) and SNR G40.5-0.5 (hadronic contributor). This analysis aims to provide new insights into the origin of the MGRO J1908+06 emission with additional VERITAS data targeted on the regions of dense molecular clouds, the application of a newly developed background estimation method for large extended gamma-ray sources, and comparisons with 12CO observation data. An energy-dependent morphology study shows that high-energy (>4 TeV) gamma rays are concentrated toward the location of PSR J1907+0602, which confirms the association with the pulsar. Meanwhile, the new VERITAS data reveals that a newly identified gamma-ray hot spot coincides with a high-density cloud, which suggests additional hadronic component in the region. Several scenarios of the gamma-ray production, which accommodate the uncertainties of distance to the accelerator candidates (including PSR J1907+0602 and SNR G40.5-0.5) mentioned in the recent literature, are also investigated. |
Monday, April 11, 2022 11:45AM - 11:57AM |
Q15.00006: Gamma-ray astrophysics with the Cherenkov Telescope Array Justin Vandenbroucke The Cherenkov Telescope Array (CTA) will provide a leap forward for very-high-energy (VHE) astrophysics, with sensitivity between 20 GeV and 300 TeV. Construction will soon begin on the "Alpha Configuration", which consists of one array in Chile for southern sky observations and one in La Palma for northern sky observations. The Alpha Configuration will achieve up to an order of magnitude improvement in sensitivity compared to today's instruments. The Astro 2020 Decadal Survey has recommended U.S. participation in CTA as part of its multi-messenger program, in particular through construction of 10 dual-mirror Schwarzschild-Couder Telescopes (SCTs), which would boost the sensitivity of the southern array. An international consortium of CTA members, led by the U.S., has constructed and operated a prototype SCT (pSCT) with a 9.7 meter primary mirror diameter. The pSCT has demonstrated the viability of the SCT concept, including an excellent measured optical point-spread function and detection of the Crab Nebula. The dual-mirror SCT design achieves excellent performance over the core energy range of CTA (100 GeV to 10 TeV). CTA will be the first open observatory in the VHE band, accepting proposals from any scientist from a country contributing financially to its construction and operation. This presentation will provide an overview of the scientific prospects for CTA in gamma-ray astronomy and multi-messenger astrophysics. |
Monday, April 11, 2022 11:57AM - 12:09PM |
Q15.00007: The Optical System for the Prototype Schwarzschild-Couder Telescope for the Cherenkov Telescope Array Deivid Ribeiro The Schwarzschild-Couder Telescope (SCT) is a candidate for Medium-Sized Telescopes of the Cherenkov Telescope Array (CTA). CTA will enable improvements in multi-wavelength and multi-messenger observations with respect to the current ground-based gamma-ray instruments, due to higher angular resolution, increased sensitivity, and energy coverage extending from 20 GeV to 300 TeV. A prototype SCT (pSCT) has been constructed at the Fred Lawrence Whipple Observatory with a novel optical system consisting of a dual-mirror design with a 9.7-m primary mirror and 5.4-m segmented secondary mirror. It has a wide field of view (about 8 degrees), allows a compact, high-resolution SiPM camera (0.067 deg per imaging pixel), and substantially improves the off-axis performance giving better angular resolution across all of the field of view with respect to single-mirror telescopes. The optical system requires a submillimeter-precision custom alignment system, which was successfully achieved with an on-axis PSF of 2.8 arcmin prior to first-light detection of the Crab Nebula in 2020. In this contribution, we report on the commissioning status, the alignment procedures, and some alignment results during the ongoing commissioning phase of the optical system of the prototype SCT. |
Monday, April 11, 2022 12:09PM - 12:21PM |
Q15.00008: The prototype Schwarzschild-Couder Telescope: performance and planned upgrade of the world’s largest dual-mirror Imaging Atmospheric Cherenkov Telescope Massimo Capasso The Schwarzschild-Couder Telescope (SCT) is a dual-mirror telescope proposed for the Cherenkov Telescope Array (CTA), the next-generation ground-based observatory for very-high-energy gamma rays. Its dual mirror technology allows to focus the light emitted in air showers on a reduced plate scale with respect to conventional single-mirror designs, enabling the use of a silicon photomultiplier-based camera with 11328 pixels, for unprecedented image resolution over a wide 8° field-of-view (FOV). The U.S.-led SCT project has built and currently operates a prototype SCT (pSCT) at the Fred Lawrence Whipple Observatory in Amado, Arizona. The pSCT features a partially-equipped camera with 1600 pixels and a FOV of about 2.7°, and has recently detected the Crab Nebula. An upgrade of the pSCT camera sensors and electronics, funded by a Major Research Instrumentation grant from the National Science Foundation, is ongoing, with the aim of fully populating the focal plane and improving the noise performance of the current prototype. In this contribution, we will introduce the CTA observatory and the proposed U.S. participation with the SCT, which has recently been endorsed in the Astro 2020 decadal survey. We will present the current status and planned upgrade of the pSCT. |
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